The present invention relates to a digital still camera and, in particular, to a digital still camera which stores an image in the form of digital data as image data and performs display processing to the image data.
A digital still camera which stores the image of an object in the form of digital data has been known. In such a camera, an image created using an optical system is converted into electric signals by optical-electric conversion elements, such as a CCD. The electric signals are converted into digital data, which is then subjected to predetermined compression processing before being stored in a memory incorporated into the camera.
Although an image photographed by a conventional camera of a film exposure type (a film exposure camera) cannot be seen until the film is developed, a photographed image by a digital still camera can be reproduced and displayed at any desired time by simply reading image data from a memory. This is advantageous and convenient for a digital still camera as it can perform operations which are impossible for a film exposure camera, including examination or erasure of photographed images.
For displaying reproduced images, a digital still camera is equipped with a display device, such as an LCD. After setting a camera in a reproduction mode, a user presses a reproduction button on the camera body, and display processing is performed to image data for one picture. Display processing specifically includes image data reading from a memory, compressed data expansion, color correction, picture size changing, and so forth. Color correction is correction with respect to discrepancies between color data for images outputted from a CCD and those to be inputted into a display device, such as an LCD. With picture size changing, the size of a picture, which is expressed by the number of pixels whose data is contained in image data for one picture (i.e., the number of horizontal pixelsxc3x97that of vertical pixels), is changed so as to fit the size of a display screen. After display processing as above, an image is displayed on a display device.
As described above, image data is subjected to display processing in response to a user command inputted for display, and a corresponding image is subsequently reproduced and displayed. The period of time between command inputting and image displaying is referred to as a reproduction waiting time, during the majority of which compressed image data is being expanded. Therefore, a high speed expansion could reduce a reproduction waiting time, which is, however, subject to limitation. In a conventional reproduction method, it has taken as long as approximately a few seconds to display a reproduced image due to a long reproduction waiting time. This forces a user to wait for a few seconds after pressing a reproduction button before having a reproduced image displayed. It has thus been long desired to reduce a reproduction waiting time to the level where a reproduced image is displayed almost simultaneously upon operation of a reproduction button by a user.
A digital still camera is further advantageously able to store a larger number of pictures than a film exposure camera. A user searching for a particular picture from among many pictures of photographed images, displays all the pictures sequentially. To be specific, the user presses a reproduction button to display one picture, and if that is not the one he wants, he again presses the button to have another picture displayed. He has to repeat this process until a desired picture appears. In this manner of searching, it takes a long time for a user to find one desired picture from among many pictures when a reproduction waiting time for one picture is long and a whole time necessary to display each picture is inevitably prolonged. With this in mind, it has also been desired to reduce a period of time necessary to display pictures for review.
The present invention has been conceived to overcome the above problems, and aims to produce a digital still camera in which a reproduced image can be promptly displayed with a reduced reproduction waiting time. The present invention also aims to provide an image reproduction and display method to be employed by a digital still camera which achieves the above object.
(1) In order to achieve the above object, according to the present invention, there is provided a digital still camera having a reproduction function for displaying an image on a display after processing image data stored inside thereof for display, comprising a memory storing image data including primary image data and secondary image data, the secondary image data requiring a shorter time for display processing than the primary image data; a primary image display processor performing display processing on the primary image data; a secondary image display processor performing display processing on the secondary image data; and a display replacer for replacing display images from a secondary image to a primary image after completion of display processing on the primary image data, the secondary image having been displayed in a reproduction mode prior to the primary image.
According to another aspect, there is provided a reproduction and display method adopted by a digital still camera for displaying an image on a display after processing image data stored inside thereof for display, comprising steps of: performing primary image display processing to primary image data; performing secondary image display processing to secondary image data, the secondary image data requiring a shorter time for display processing than the primary image data; and replacing display images from a secondary image to a primary image after completion of display processing on the primary image data, the secondary image having been displayed.
It should be noted that primary image data is used to obtain a normal photographed image, and preferably allows accurate reproduction of an originally photographed image with high image quality. Primary image data may be either non-compressed data or compressed data which has been compressed using a predetermined compression method.
Secondary image data can be processed for display in a shorter period of time than primary image data. High image quality, such as resolution, is not required for secondary image data, as reproduction of an image which is clear enough to distinguish a photographed object is the aim of the secondary image data.
For instance, secondary image data is image data whose data volume has been curtailed to an extent that a reproduced image based thereon is still capable of distinguishing a photographed object. Preferably, secondary image data may be non-compressed data with the data volume reduced, for instance, in sampling processing in which some pixel data are removed, as non-compressed data can be processed for display in a significantly shorter period to time compared to compressed data. Alternatively, compressed data having a reduced data volume may be employed since data having a smaller volume will be processed in a shorter time.
The present invention has been conceived in view of the following facts. Image reproduction based solely on primary image data achieves high quality images but needs a longer reproduction waiting time, whereas image reproduction based solely on secondary image data achieves reduction of a reproduction waiting time but reproduces images with only poor quality. That is, it is difficult to reproduce an image with high quality in a shorter reproduction waiting time based solely on image data of either one of the above two types. In view of the above, this invention is constructed to utilize advantages of image data of both types.
According to this invention, a secondary image picture is first displayed in a reproduction mode and, after completion of display processing for primary image data, the secondary image picture being displayed is replaced by a corresponding primary image picture. Since display processing for secondary image data is short, secondary image pictures can be displayed with only a short reproduction waiting time. The secondary image picture being displayed is automatically replaced by a primary image picture, as mentioned above. With this arrangement, a user barely has to wait until an image is displayed, and he can know the details of a photographed image by examining a primary image picture. The present invention therefore enables both reduction of a reproduction waiting time and displaying of a high quality image. This can increase the product value of a digital still camera.
(2) According to another aspect, in the reproduction and display method as defined above, display processing of primary image data corresponding to a secondary image which is then being displayed is stopped when a predetermined command is externally inputted; and another secondary image is displayed.
According to this aspect, the present invention is quite beneficial for a user who searches a desired picture from among many photographed images by sequentially displaying them. Specifically, a secondary image picture is displayed as soon as a user inputs a command, so that the user reviews it to check an object shown thereon as to whether or not the picture shown is his desired one. If it is not the picture he wants, he inputs another display command. In response to this command, ongoing display processing for a corresponding primary image data is halted and image data for the next secondary image picture is subjected to display processing so that the next secondary image picture is displayed. When the user finds a desired secondary image after repetition of the above process, he stops advancing pictures so that display processing for corresponding primary image data continues to completion. Then, the secondary image picture being displayed is automatically replaced by a relevant primary image picture, so that the user can examine the details of the photographed image by referring to the primary image. As described above, the present invention achieves significant reduction of a period of time necessary for a user to search for a desired photographed image and to examine the details thereof.
(3) In some conventional digital still cameras, non-compressed index image data, such as thumbnail image data, is stored separately from compressed image data. When the present invention is applied to such cameras, index image data may also be used as secondary image data. In such use, display processing for secondary image data may include processing to change the size of index display image data.
Index image data is inherently used for displaying a plurality of pictures simultaneously on a display device when image data is processed by a computer, and suchlike. In this use, high image quality is not absolutely required as each picture is only displayed in a small size, and there is more demand for a shorter processing time before a plurality of pictures are simultaneously displayed. Thus, index image data is generated in sub-sampling processing in which pixel data of original image data is removed, so as to have a smaller data volume. For instance, the data volume of primary image data is a few hundred Kbytes, while that of index image data is {fraction (1/10)} thereof or else.
Index image data is usable only to generate a rough image picture which at most distinguishes an image shown thereon, and its resolution is too low to clearly present details or photographed conditions of the image. Index image data hardly allows reproduction of high quality image which is necessary for thorough examination of details. However, it advantageously allows display of an image in a short time as it is non-compressed and has a small data volume. Index image data is therefore preferably used as secondary image data of this invention.
When index display image data is used also as secondary image data unique to the present invention, it is unnecessary to generate image data of another type which has not been conventionally used or to secure memory area for storing such image data within a memory.
It should be noted that the object of this invention can also be achieved by using non-compressed image data which allows reproduction of an image with suitable resolution for the image display device of a camera, stored for use solely in a reproduction mode. With this structure, replacement of a secondary image picture by a primary image picture is unnecessary. However, such image data must have decent resolution, and therefore a relatively large data volume is inevitable so as to match a display device. Even worse, since memory area must be secured for those data, which has a large volume, the number of pictures whose data can be stored in the memory is accordingly reduced. This is contrary to one of the advantages of a digital still camera, i.e., capability to store numerous pictures, and thus not preferable. On the contrary, in this invention, the number of pictures whose data can be stored is not adversely affected as above when secondary image data, having a small data volume, is stored together with primary image data.
(4) In this invention, a memory may be either of a detachable type, like a detachable memory card, or a non-detachable type with respect to a camera. A flash memory is often used for the memory. Alternatively, any other medium accessible in an electric, magnetic, or optical method may be applied, such as a semiconductor memory, an IC card, a magnetic disc, RAM, and a magnetic tape.
Also, primary image data and secondary image data may be stored in the same memory or different memories. Memory areas for primary and secondary image data may be arranged as desired.
Display processing for secondary image data may be performed prior to that for primary image data, or both may be performed in parallel.